🚀 go-pugleaf

In <1b30clINN7u1@usenet.INS.CWRU.Edu> an938@cleveland.Freenet.Edu (George II Lenzer) writes:


>	I would like to know how those motion sensing yard lights
>work.  Are they based on IR sensing?  Does anyone have a schematic?
>I would like to build one for use indoors.

I once built one. It uses some kind of ceramic that changes resistance
(or generated a current) when the temperature changes. A special lens
is used to focus "warmth-beams" onto this part.

The information (resistance/current) is fed into an analog
differentiator and a schmitt trigger.

So, when someone, whose temperature was different from the environment,
enters the view-field of the device, the resistance changes (a current
was generated), this generates a signal on the output of the
differentiator, which, if strong enough, triggers the trigger.
The schmitt-trigger is needed to avoid a "hit" due to a rise in ambient
temperature (You only want to have light if a person enters the
view-field, i.e. when a sharp increase of tempereture is detected).

When using indoors, You have to be carefull. I once had it set up, so
that when the sun rose on a sunny day, the first beam of sunlight that
hit the ground in front of the sensor (it was in the basement of my
house) triggered the alarm B-{)
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